Filter apparatus for gas scrubber



United States Patent Inventor Appl. No.

Filed Patented Assignee FILTER APPARATUS FOR GAS SCRUBBER 13 Claims, 4Drawing Figs.

US. Cl

Int. Cl. Field of Search B01d47/l6 [56] References Cited UNITED STATESPATENTS 3,348,825 10/1967 Mcllvaine S5/257X 3,488,039 1/1970 Ekman v.261/112X Primary ExaminerFrank W. Lutter Assistant Examiner-Vincent 1-1.Gifford Attorney-Mason, Kolehmainen, Rathburn & Wyss ABSTRACT: Filterapparatus for a gas scrubber comprising a plurality of elongated filterelements extending transversely across a flow passage and defining aplurality of separate flow paths between adjacent elements. Firstsupport means is provided for maintaining a first group of said elementsin a fixed position in said flow passage and second support means isprovided for supporting a second group of said elements for movementtoward and away from said elements of said first group to increase anddecrease the spacing or area defining said separate flow paths betweenadjacent elements in response to the flow pressure or buoyancy of saidgas moving through said scrubber.

FILTER APPARATUS FOR GAS SCRUBBER The present inventionrelates to a newand improved filter apparatus for a gas scrubber, more particularly agasscrubber of the type adapted for using scrubbing liquid (usuallywater) which is introduced into the gas flow to agglomerate and collectthe contaminant particles therein.

The present invention comprises an improvement on the filter bedstructure illustrated and described in U. S. Pat. No. 3,348,825 and incopending U.S. Pat. application Ser. No. 730,517 now US. Pat. No.3,488,039, filed May 20, l968. In the gas scrubbing apparatus describedin the aforementioned copending US. Pat. application, there is provideda filter bed with a plurality of individual, separately supportedelongated filter elements which are arranged in a novel frame structurefor limited free floating movement toward and away from ad jacentelements, and with and against the direction of gas flow. In the presentinvention, a plurality of elongated filter elements, such as rods, tubesor pipes, and the like, are arranged in parallel, spaced-apart relationto provide a plurality of narrow slots or flow passages for producing ahigh velocity flow of gas through a reduced area nozzle section in thescrubber housing. A first group of the filter elements are fixedlysupported within the nozzle section in parallel arrangement on a commonplane, and a second group of elements, spaced alternately between theelements in'the firstgroup, are supported on a separate framework whichis movable between limits toward and away from the elements of the firstgroup in a direction parallel to the general direction of gas flowthrough the scrubber.

In many installations, for example, when gas scrubbers are used fortreating gases generated in iron-melting cupola furnaces, steel-meltingopen-hearth furnaces, electric furnaces and the like, it is desirable toclosely correlate the quantity or volume of gas withdrawn from thefurnace housing with the volume of input or blast air supplied to thefurnace. Regulation of the volume of gas removed affects the amount ofair which can infiltrate through the charging doors of the furnacestructure and one method of accomplishing control of gas flow in and outof a furnace is by the installation of a flow meter on the input orair-blast duct and in the outlet duct or hood lead ing to the gasscrubbenSignals from the input and output flow meters are electronicallyintegrated and the resulting impulse is used for controlling a damper orthe like positioned in an outlet or exhaust duct from the gas scrubber.in high efiiciency, wet-type gas scrubbers, such as those shown anddescribed in the aforementioned US. Pat and in the copending US. Pat.application previously mentioned, the collection efficiency orpercentage of contaminant particles separated out of the gas is in adirect relation to the velocity of the gas passing through the filterbed of the scrubber. The gas velocity in turn is a measure of thepressure drop in the system and, with higher pressure drops, more poweris required and operating costs are likewise higher.

In order to maintain a desired minimum efficiency, or percentage ofcontaminants removed from the gas in installations where the gas flowrate varies over a range, it is necessary to adjust the flow area of theventuri region in the gas scrubber to maintain the velocity within ausable range. Presently, some wet scrubbers employ electrical .means forsensing the velocity of the gas flow in the critical flow areas of thescrubber, and signals produced by these electrical sensing devices areintegrated electrically and used for controlling powered mechanicalmeans which are effective to expand and contract the effective flow areafor the gas and thereby to control and maintain the gas velocity in adesirable range. In the aforementioned U.S. copending Pat. application,the filter elements are individually movable within a limited distanceso that the spacing between adjacent elements is adjusted and variedfrom time to time in accordance with the input of gas to the scrubber sothat the velocity is maintained relatively constant.

The present invention comprises an improvement over previous types ofself-adjusting filter beds as described and includes means forsupporting two groups of alternately spaced, elongated filter elementsand biasing one group of elements against the buoyant force of thehighvelocity gases so that the elements automatically open and close thespacing between adjacent pairs in response to the volume of gas suppliedthereby maintaining a relatively constant gas velocity. With arelatively uniform gas velocity, the efficiency of particle separationis relatively uniform even though the flow rate or volume of gas beinghandled by the scrubber varies over a wide range. Theautomatic,self-adjusting filter bed apparatus of the present invention does notrequire elaborate electronic sensing devices and circuitry and thuseliminates much costly equipment. Also, the gas scrubber of the presentinvention is extremely effective for a wide variety of applicationswherein many different types of contaminants and impurities are encountered and wherein the flow rate of gas to be treated varies widely.

It is an object of the present invention to provide a new and improvedgas scrubber and filter apparatus therefor.

Another object of the present invention is to provide a new and improvedgas scrubber and filter apparatus of the character described wherein thevelocity of gas flow between adjacent filter elements is maintainedwithin a desired range even though the flow rate or volume of gasesbeing treated in the gas scrubber varies widely.

Still another object of the present invention is to provide a new andimproved automatic, self-regulating filter apparatus for a gas scrubberwhich provides a substantially constant range of gas velocity throughthe apparatus, even though the volume flow rate of gases being treatedchanges widely.

The foregoing and other objects and advantages of the present inventionare accomplished in an illustrated embodiment thereof comprising a gasscrubber employing a new and improved filter apparatus including aplurality of elongated filter elements mounted in spaced-apart,parallel, side-by-side relation generally transversely across a narrowflow path or nozzle structure. Each filter element includes asubstantially largeexterior surfacearea and means are provided forwetting the elements with scrubbing liquid so that the contaminantparticles and impurities in the gas passing around the elements impingeagainst the liquid film and are agglomerated and collected in theliquid. A first group of filter elements is supported in fixed relationin the flow path defining structure of the scrubber and a second groupof filter elements is provided with the filter elements thereof spacedalternately between pairs of adjacent elements of the first group. Theelements of the second group are supported on a framework which ismovable toward and away from the elements of the first group to increaseand decrease the spacing between elements to maintain a relativelyconstant gas velocity. Should the volume flow rate of gases beingtreated in the scrubber increase, the buoyant pressure force of thegases acting on the filter ele ments of the second group increases andthese elements are moved away from the elements of the first groupthereby increasing the effective flow areaor spacing between elements tomaintain a relatively constant gas velocity. Should the volume flow rateof gas decrease, the buoyant force decreases correspondingly and thesecond group of filter elements are biased in the opposite direction todecrease the spacing of effective flow area between adjacent elements sothat the velocity is maintained at substantially the same value. Theparticle separation efficiency being dependent on gas velocity ismaintained relatively constant, even though the volume flow rate ofgases introduced into the scrubber varies widely from time to time.

For a better understanding of the present invention, reference should behad to the following detailed description taken in conjunction with thedrawings, in which:

FIG. 1 is a vertical sectional view illustrating an updraft, wet-typegas scrubber employing a new and improved filter apparatus constructedin accordance with the present invention.

FIG. 2 is a transverse, horizontal cross section taken substantiallyalong line 2-2 of FIG. 1;

FIG. 3 is an enlarged, vertical, sectional view taken substantiallyalong line 3-3 of FIG. 2 and showing the filter elements in an operatingposition with minimal spacing between elements; and

FIG. 4 is a sectional view similar to FIG. 3 showing the filter elementsin another operative position with maximum spacing between elements.

Referring now, more specifically, to the drawings, therein isillustrated one embodiment of a new and improved updraft, wet-type gasscrubber which is adapted to use scrubbing liquid, such as water, foragglomerating and removing contaminants and other impurities from gas.The gas scrubber 10 includes an upstanding housing structure comprisinga plurality of vertically stacked, sections 12, 14 and 16, respectively,and is supported from the floor or other surface on a plurality of legsor posts 18 extending downwardly from the lower housing section 12.

The lower housing section 12 includes vertical, upper sidewalls 20 andlower, inwardly and downwardly sloping walls 22 which form a liquid sump24 at the lower end of the housing. The sloped walls 22 converge towardan outlet or drain opening defined at the upper end of a flanged drainfitting 26 and the scrubbing liquid and contaminants collected thereinare removed from the liquid sump 24 through a drain or sewer line 28running to a sewer or sludge removal system.

Contaminated gas to be treated in the scrubber 10 is directed into thelower section 12 of the housing through an inlet fitting 30 extendingthrough an opening in one of the sidewalls 20, and the outer end of thefitting is connected to a supply duct 32 or other source of contaminatedgas. As shown by the arrows A in FIG. 1, the contaminated gases directedinto the scrubber through the inlet fitting 30 move upwardly into thenext adjacent intermediate housing section 14 and the intermediatehousing section includes a nozzle portion 34 between the upper and lowerends having a transverse crosssectional area which is substantially lessthan the transverse area at the upper or lower end of the housingsection. The upwardly moving contaminated gases flow at increasedvelocity as they pass through the reduced area nozzle section 34 andbelow the nozzle 34, the housing 14 is provided with upwardly andinwardly sloping sidewalls 36. The nozzle section 34 includes verticalouter sidewalls 38 and upwardly and outwardly sloping sidewalls 40extend upwardly thereof to the upper end of the housingsection 14.

As best shown in FIGS. 2, 3 and 4, the reduced flow area nozzle section34 is provided with a peripheral inner framework 42 formed of channelmembers having upper and lower horizontal flanges extending outwardlytoward and joined at their outer edges to the inside surfaces of thevertical walls 38. The framework 42 includes four channels joined atright angles to one another to form a square or rectangular shaped, highvelocity throat or flow passage 44. The walls of the flow passage 44 aredefined by vertical webs 44a FIGS. 2 and 3) of the channels, and thetransverse cross-sectional area bounded by the webs 44a is substantiallyless than the transverse or horizontal cross-sectional area of thehousing section 14 at either end, so that the velocity of the gas in thenozzle section 44 is substantially greater than the average flowvelocity in other portions of the scrubber housing.

In accordance with the present invention, the reduced area flow nozzlesection 34 is provided with a plurality of horizontal spaced-apartparallel, elongated filter elements 48-1 and 48-2. The filter elements48 may comprise rods or hollow tubes or sleeves preferably formed ofstainless steel or other corrosion resistant material. When stainlesstubes are used they are mounted on axles 50 and are freely rotativetherewith about the longitudinal axes of the elements as the gases flowupwardly through the slots or spaces between adjacent elements. Thefilter elements 48-1 comprise a first group supported in fixed relationin the reduced area nozzle structure 34 and opposite ends of the axles50 project outwardly into and are supported in spaced openings 44bdrilled in the webs 44a of a pair of facing channel members. The filterelements 48-2 comprise a second group and are spaced alternately betweenpairs of elements 48-1 in the first group. Each individual filterelement 48-1 in the first group is free to rotate about its longitudinalaxis but is restrained against vertical and horizontal movement relativeto the channel framework 42 of the nozzle section 34 as the gases passupwardly between the elements at high velocity.

The filter elements 48-2 in the second group are spaced alternatelybetween the elements 48-1 and are mounted on a rectangular frame 52formed of vertical plates 52a and one pair of oppositely facing platesis provided with outwardly extending horizontal support flanges 52b. Theplates 52a are parallel with the inside webs 44a on the channels of theframework 42 and the flanges 52b are parallel to and spaced above theupper flanges of the channels.

As best shown in FIGS. 3 and 4, the lower edges of one pair of parallelplates 52a perpendicular to the elements 48 are provided with spacedapart, teethlike downward projections 53 for supporting opposite ends ofthe axles 50 which carry the filter elements 48-2 of the second group.The spacing between the projections or teeth 53 is sufficiently wide topermit both groups of filter elements 48-1 and 48-2 to lie in the samehorizontal plane with the elements 48-] projecting outwardly beyond theteeth without touching or interference. The filter elements 48-2 in thesecond group are movable in a vertical direction from a lower positionshown in FIG. 3, wherein a minimum spacing s is provided betweenadjacent pairs of elements 48-1 and 48-2 to an upper position wherein amaximum spacing A is provided between the closest surface areas onadjacent pairs of elements 48-1 and 48-2. When a low volume flow rate ofgas is introduced into the scrubber 10, the upward buoyant force of thegas passing through the nozzle section 34 is relatively low and thefilter elements 48-2 remain in the lower position, as shown in FIG. 3,with the minimal spacing s obtaining and, accordingly, a relativelysmall, effective flow area is provided between the elements, resultingin a relatively high velocity of gas flow between each pair of adjacentelements 48-1 and 48-2. When the volume flow rate of gas introduced intothe scrubber is increased substantially the greater buoyant upward forceof the flowing gases tends to move the filter elements 48- -2 in thesecond group upwardly from the position in FIG. 3 toward the position ofFIG. 4, and this increases the spacing between elements as representedby letter A Accordingly, the effective flow area between each pair ofelements is increased and the gas velocity between each pair of elementsis maintained at substantially the same value as before even though theflow rate or volume has been greatly increased. The buoyant force of theupwardly flowing, high velocity gas lifts the elements 48-2 in thesecond group upwardly in an amount roughly proportional to the volume ofgas supplied to the scrubber and the framework 52 which supports theelements in the second group maintains all of the elements in a commonplane as they move up and down. The amount of displacement of theelements is responsive to the volume input of the gas and thedisplacement varies correspondingly to automati'cally maintain arelatively constant high velocity of gas flow between the adjacent pairsof filter elements 48-1 and 48-2.

The angle framework 52 which supports the second group of filterelements 48-2 is biased toward the downward or minimum spacing positionof FIG. 3 by means of a plurality of compression springs 54 which aremounted beneath the upper flange of the channels of the framework 42 andoutwardly of the web portions 44a thereof. The springs are effective tomaintain and return the minimal spacing s between elements whenever thevolume flow of gas into the scrubber is low and thereby maintain aminimum gas velocity between elements so as to obtain good separationefficiency. Each spring is held in centered position by a verticalcenter pin or bolt 56 in coaxial alinement with the coils of the spring,and the bolts extend upwardly through opening in the upper flange on thechannels of the frame 42 and through alined openings or holes'in theflanges 52b of the movable framework 52 which supports the second groupof filter elements 482. Bearing washers 58 are provided at the lower orhead end of the bolts 56 to engage the lower ends of the springs 54 andthe upper ends of the springs bear against the underside of the upperflanges of the channels of the framework 42. Resilient cushioningwashers 60 are provided to cushion the shock between the flange portions52b of the upper frame 52 and the upper flanges of the channels of thelower framework 42 as the framework 52 moves up and down in response toincreases and decreases in velocity of the gas. The washers 60 also setup the value of minimum spacing s between the elements in cooperationwith the tightening or loosening of the compression on. the springs 54.Pairs of adjusting nuts 62 are provided for selecting thedesired amountof compression on the springs 54 to provide for a desired minimumvelocity value of the flowing gas which will instigate upward movementof the second group of elements. The spacing between adjacent pairs offilter elements 48--] and 48-2 in the flow nozzle structure 34 isautomatically self-regulated or adjusted to adapt to the instantaneousflowrate of the gases being handled by the scrubber l0 and the flowvelocity is maintained at a relatively constant value to insure a highcollection efficiency.

After moving through the reduced area flow nozzle structure 34, thegases expand and slow down and then pass into an upper filter bed 66mounted at the lower end of the upper housing section 16. The filter bed66 includes a plurality of spherical filter elements 68 arranged severallayers deep and the elements are supported on a screen or mesh 70. Thegases flowing through the filter bed 66 pass through many diverse andtortuous paths around the surfaces of the individual filter elementsand, accordingly, the gas accelerates and decelerates and changesdirection rapidly.

In order to collect and agglomerate the dust particles and othercontaminants and fumes in the gas and remove this material from the gas,a scrubbing liquid (usually water) is introduced into the gas from aplurality of spray nozzles 72 positioned below the filter elements 48-land 48-2 to direct a spray of finely divided liquid upwardly onto thesurfaces of the filter elements. The scrubbing liquid is supplied to thespray nozzles 72 through a piping manifold 74, and the spray nozzles arepreferably of the atomiz'in'g type which direct a finely divided sprayof mist onto the surfaces of the filter elements 48 l, 482. Because ofthe high velocity of gas flow around and adjacent the surfaces of thefilter elements, the finely divided liquid droplets are entrained intothe gas flow andthe dust particles and other contaminants in the gas arewetted with liquid and collect and agglomerate in the liquid droplets.

The wetted gases move upwardly through the flow nozzle structure 34 andinto the filter bed 66 wherein further agglomerations and collections ofthe contaminant particles into the liquid droplets take place. Becausethe upwardly flowing gases passing into the filter bed 66 are wetted,the surfaces of the spherical filter elements68 are wetted with a thinliquid film and the dust particles and contaminants impinge on theliquid film and are collected and agglomerated in the liquid. Individualliquid droplets begin to grow in size and become heavily laden withcontaminants and this liquid is drained off through a line 75 to thesump 24;

An intense foaming action takes place in the upper levels or layers ofspherical filter element in the filter bed 66 wherein a maximuminterchange of dust and contaminant particles from the gases into thescrubbing liquid or bubbles takes place. The upper level of foamingaction above the filter bed 66 is maintained by means of the drain line75 and a scupper-type center drain 76 having a discharge pipe 78 and asock-type rubber valve member 80 which opens periodically to dischargeaccumulated liquid in a relatively large quantity downwardly toward thesump 24.

After the gases have passed upwardly through the filter bed 66 and thefoaming layer adjacent the upper portion of the bed, almost all of thecontaminants have been removed; however, the gas still contains someliquid droplets and mist which should be removed from the gas beforedischarge from the scrubber. For this purpose, a rotary demist vaneassembly 81 is mounted in the upper section of the housing 16 above thefilter bed and the vane assembly includes an annular ring of demistingvanes 82 which imparta high velocity spiral flow direction to the gases,as indicated by the arrow B. The vanes 82 are sloped to direct the gaseshorizontally outwardly toward the inside surface of a perforated, innercylinder 84 having a large number of perforations therein. Because theliquid droplets are heavier than the gas, they are centrifuged outwardlyby the vanes 82 with greater force and readily pass through theperforations in the cylinder 84, eventually collecting and impinging onthe inside walls of the housing section 16. These liquid droplets thenflow downwardly and collect in an annular trough 86 formed around theinside of the housing section outwardly of the outer ends of the vanes82. Collected liquid is drained periodically from the trough 86 througha drainpipe 88 having a sock-type valve 90 therein, and this liquid isdirected into the filter bed 66. The annular ring of sloped demistingvanes 82 centrifugally separates the liquid droplets and liquid mistfrom the gases and the liquid is collected and reused in the filter bed66. The swirling gases, after having the liquid mist removed, passupwardly in the perforated cylinder 84 and eventually are dischargedfrom the scrubber through an opening at the upper end of the housingsection via an outlet or discharge fitting 92. The fitting 92 isconnected to an elbow 94 and downtake duct 96, or other suitableductwork. A fan (not shown) is connected on the inlet or outlet side ofthe scrubber to supply the motive power for moving the gases through thescrubber. The perforated cylinder 84 serves to hide the separated outliquid from the upwardly swirling gas stream and prevents recombinationof the liquid and gas.

The gas scrubber 10 of the present invention provides a new and uniqueautomatically self-regulating filter apparatus for using a high velocityof gas flow through the apparatus even though the volume or flow rate ofgas introduced into the scrubber varies widely. Automatic spacingadjustment between elements in the filter apparatus provides for auniform, high efficiency removal of contaminants from the gas eventhough the volume flow rate of gas introduced into the scrubber variesgreatly from time to time.

I claim:

1. In a gas scrubber having a flow passage for contaminated gas, a selfadjusting filter apparatus comprising a plurality of elongated filterelements extending transversely across said flow passage and defining aplurality of separate flow paths between each pair of adjacent elements,first support means for maintaining a first group of alternate ones ofsaid elements in fixed relation in said flow passage and second supportmeans for supporting at least one element in a second group comprisingthe remainder of said elements for movement toward and away from saidelements of said first group to increase and decrease the spacingbetween at least one adjacent pair of elements inresponse to the flowpressure on said elements by said gas moving through said passage.

2. The apparatus of claim 1 wherein said filter elements are mounted onsaid first and second support means for free rotation about theirlongitudinal axes.

3. The apparatus of claim 1 including resilient means for biasing saidsecond group of'elements toward said first group of elements to decreasethe spacing between adjacent elements and oppose the forces exerted onsaid second group of elements by the flow pressure of said gas acting onsaid elements as it moves through said flow passage.

4. The apparatus of claim 3 wherein said resilient means comprises atleast one spring means interconnected between said first and secondsupport means.

5. The apparatus of claim 3 wherein one of said support means comprisesan annular frame means defining a wall portion of said flow passage andincluding opposite side members supporting opposite ends of said firstgroup of elements.

6. The apparatus of claim wherein the other of said support meanscomprises annular frame means having opposite side members supportingopposite ends of said second group of elements, said resilient meanscomprising a plurality of spring members interconnecting said framemeans.

7. The apparatus of claim 1 wherein said elements are parallel and saidsecond group of elements are movable from a position of minimum spacingbetween all elements lying on a common plane with said first group ofelements to a maximum-spacing position wherein said second group ofelements are displaced from said first group in the direction of gasflow.

8. The apparatus of claim 1 including means for limiting the movement ofsaid second group of elements relative to said first group. 4

9. A gas scrubber comprising a housing defining a flow passage, a filterapparatus in said housing including a plurality of parallel elongated,spaced-apart filter elements extending across said flow passage, firstsupport means for supporting opposite ends of a first group of alternateones of said ele ments in a fixed position relative to said flow passagehousing,

and second support means for supporting at least one element in a secondgroup comprising the remaining elements for movement relative to saidelements in said first group to vary the spacing between elements ofsaid first and second'group in response to flow pressure of gas actingon said second group of elements during passage through said filterapparatus.

10. The gas scrubber of claim 9 wherein said second support meanscomprises annular frame means having oppositeside members for supportingopposite ends of the elements of said second group and resilient means,biasing said frame means in a direction toward the elements in saidfirst group to reduce the spacing between adjacent pairs of elements insaid groups 11. The gas scrubber of claim 10 wherein said eleme'n ts aresupported for free rotation about their longitudinal axes and aredisposed in a common plane to provide minimum spacing between adjacentelements and wherein said second group of elements is movable in adirection with the gas flow through said scrubber out of said commonplane for increasing said spacing in response to gas flow pressureacting thereon as it moves through said filter apparatus.

12. The gas scrubber of claim 10 including means for adjusting the valueof biasing force exerted by said resilient means.

13. The gas scrubber of claim 10 wherein said resilient means comprisesa plurality ofsprings connected between said first and second supportmeans.

